hive-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Tucker, Matt" <Matt.Tuc...@disney.com>
Subject RE: Map side join
Date Wed, 13 Jun 2012 15:20:06 GMT
Hi,

Assuming that 4 tables are small enough to fit in the Distributed Cache, the joins between
the tables all need to join against a common key.

Example:
set hive.auto.convert.join=true;
SELECT *
FROM large
    JOIN smalla ON
        large.key = smalla.key1
    JOIN smallb ON
        large.key = smallb.key2
    JOIN smallc ON
        large.key = smallc.key3
    JOIN smalld ON
        large.key = smalld.key4;

Having a different join key will push the join off into a different task, as will the order
of the join condition. In this example, large.key was always on the left side of the join
conditions.


Matt Tucker

-----Original Message-----
From: Abhishek [mailto:abhishek.dodda1@gmail.com] 
Sent: Wednesday, June 13, 2012 11:13 AM
To: user@hive.apache.org
Subject: Map side join

Hi all,

How map side join in hive, can be used to join multiple tables(suppose 5 tables).

Regards
Abhishek 

Sent from my iPhone

Mime
View raw message